In instances of severe pain, infection, and other medical ailments, it has been proven beneficial to administer a continuous flow of medicinal fluid to a patient through a catheter-based system. There are many types of medicinal fluids that can be administered in this manner including, but not limited to, insulin, analgesics and antibiotics.
The continuous delivery of such medicinal fluids over extended periods of time has required prolonged hospital stays and monitoring by medical staff. Devices for this purpose have been designed to be fairly mobile and provide for a continuous or basal rate of fluid, which is the on-going continuous primary flow rate of fluid to a patient.
However, one problem that is not successfully addressed is readily determining whether the flow of fluid to the patient has been altered or interrupted. Very often, the rates of flow are in the range of from about 1 to about 14 cubic centimeters of fluid per hour. At such low flow rates, it is difficult to determine if the flow is inadvertently altered or interrupted by, for example, material collecting in a filter, orifice, connection, or in a flow regulator to block or alter the flow rate. Alternatively and/or additionally, the flow path may become pinched, constricted or kinked to alter or interrupt the flow rate. An interruption in flow alters the pressure of fluid in the tubing.
Various hydrostatic manometers have been developed that may be directly placed in the tubing line and that may be operated to temporarily interrupt the fluid flow so that hydrostatic pressure measurements may be periodically taken. See, for example, U.S. Pat. No. 3,807,389 to Miller et al. These types of in-line manometers measure hydrostatic pressure and require periodic interruption of the fluid flow, such as by a stopcock, to obtain a pressure reading. This is inconvenient in some situations and may even be hazardous if the required pressure level drops or rises significantly between readings, resulting in over- or under infusion.
An in-line, hydrodynamic manometer for measuring infusion pressures is described in U.S. Pat. No. 4,282,881 to Todd et al. This manometer uses a closed pressure-measuring chamber containing a nonexpansible volume of air, which is in communication with a passage through which fluid, whose pressure is to be measured, flows. Several problems exist with this manometer design. For example, the entire apparatus is rather large in order to accommodate a pressure-measuring chamber long enough to measure a given range of pressures. The manometer, as illustrated in FIG. 1 of U.S. Pat. No. 4,282,881, is large enough to require support on a stand.
There are numerous markings on the housing of the manometer, as shown in FIG. 2 of U.S. Pat. No. 4,282,881, which correspond to various hydrodynamic pressure readings of the fluid flowing through the passage. Again, this results in the need for a relatively long pressure-measuring chamber and thus a relatively large manometer apparatus. Furthermore, because the pressure of intravenous infusions is typically low, from approximately 6 psi at the fluid source to approximately 0.3 psi at the patient's vein, clinical personnel generally do not care about, nor do they need to know, absolute hydrodynamic pressures during intravenous (“IV”) infusion of fluid.
What is clinically important is whether and when the flow is in one of three states: 1) flowing relatively freely; 2) obstructed by a distal blockage (i.e., downstream from the manometer, typically at the site of insertion of the catheter into the patient); or 3) not flowing at all, either because the infusion is turned off or there is a proximal obstruction (i.e., upstream from the manometer, typically close to the fluid source and/or within the associated delivery tubing). Thus, the traditional manometer scale with a wide array of absolute pressure markings is, generally, clinically unnecessary.
An improved manometer is described in U.S. Pat. No. 6,371,937. This device functions as a conventional manometer with a pressure-measuring chamber but includes an additional space-saving chamber connected to the pressure-measuring chamber that allows the manometer to be much smaller than conventional devices. Fluid flows through the device and also enters the pressure-measuring chamber where it reaches a level through compression and expansion of air in both the pressure-measuring chamber and space-saving chamber. This scaled down device includes simple markings corresponding to fluid flow states. However, the device is still a manometer and required fluid to enter a pressure-measuring chamber. Moreover, the device must be aligned and oriented properly to obtain a reading. That is, the flow state of fluid within the passage is determined by an examiner, typically a nurse or other caregiver, by ascertaining where the leading edge, or top, of the fluid column within the pressure-measuring chamber is in comparison to certain reference markings that are associated with, and are present alongside, the pressure-measuring chamber. In addition to these problems, at very low flow rates and/or very low pressures (e.g., essentially atmospheric pressures) changes in the flow rate or pressure are difficult to detect.
What is needed is a simple, mobile device to provide a continuous and substantially constant flow of medicinal fluid and indicate a fluid flow condition in a clear, discrete and easy to identify manner. Further, a simple and effective device that indicates a fluid flow condition in a clear, discrete and easy to identify manner such that it can be readily identified by even a busy care provider or an infirm patient.
Accordingly, there is a need for an indicator assembly that can be readily integrated into liquid dispensing systems, and more specifically to a catheter-based system for infusing a liquid into the body of a patient and which is easy to view and read properly and function at low flow rates of less than 14 cubic centimeters of fluid per hour, desirably between 1 and 14 cubic centimeters per hour. There is also a need for an indicator assembly that can be readily integrated into a catheter-based liquid dispensing system for infusing a liquid into the body of a patient and which is easy to view and read properly and function at relatively low flow rates and at pressures less than about 4 pounds per square inch (28 kilopascals).
A need exists for an indicator assembly that be readily integrated into a catheter-based liquid dispensing system for infusing a liquid into the body of a patient that is simple, reliable and accurate. A need also exists for an indicator assembly that be readily integrated into a catheter-based liquid dispensing system for infusing a liquid into the body of a patient that is simple, reliable and accurate at indicating predetermined pressures as well as easy to understand. There is also an unmet need for a pressure change indicator assembly that conveys a simple and easy to see and understand signal about a change in a fluid flow condition.